1. Field of the Invention
The present invention relates to an improved combination structure of an oil-impregnated bearing and a rotor shaft, especially, an oil-impregnated bearing is positioned in an axle tube in a non-tight fit manner, thereby allowing pivotal connection of the rotor shaft, and a retained is used to prevent the lubricating oil in the axle tube from leaking, and meanwhile, prevent the shaft of the rotor from detaching from the axle tube.
2. Description of the Related Prior Art
A conventional heat-dissipating fan or brushless motor includes a rotor having a shaft pivotally held by a bearing. Commonly used bearings include ball bearings or oil-impregnated bearings (self-lubricating bearings). An oil-impregnated bearing is generally tightly secured to the inner periphery of an axle tube or bearing seat for pivotally holding the rotor shaft. It is, however, found that the oil-impregnated bearing is compressed in the radial direction and thus results in deformation in the inner periphery of a center hole in the oil-impregnated bearing. As a result, non-smooth friction occurs between the rotor shaft and the inner periphery of the hole in the oil-impregnated bearing. Although such a deformation is relatively small, rotational noise tends to occur under continuous operation of the rotor shaft at a high speed. In addition, a gap between the rotor shaft and the inner periphery of the hole in the oil-impregnated bearing becomes larger due to the continuous non-smooth friction. Vibrations occur during rotation of the rotor shaft and greater noise is thus generated. The operating life of the bearing is accordingly shortened.
The U.S. Pat. No. 5,610,462 to Takahashi, filed on Jun. 20, 1994, disclosed a brushless motor in which an oil-impregnated sleeve bearing is inserted in a bearing holder having a cylindrical shape with a closed bottom, and a rotating shaft is inserted in the oil-impregnated sleeve bearing in such a manner that the rotating shaft may freely rotate. Nevertheless, some of the elements are difficult to manufacture, such as the boss 58 and the cut-away portions 46d1 of the rotor, as the boss 58 and the cut-away portions 46d1 must mate with each other precisely in order to prevent oil leakage and to provide an easy assembly procedure.
The U.S. patent application Ser. No. 09/563,955, U.S. Pat. No. 6,336,745 filed on May 2, 2000, entitled by xe2x80x9cOil-impregnated Bearing and Rotor Shaft Combinationxe2x80x9d, discloses an oil-impregnated bearing combination. The inner peripheral of the upper end of the axle tube 1 is tightly fitted with an upper cap 12 having an opening 121. After the rotor shaft 3 passes through the opening 121 of the upper cap 12, a retainer 32 such as a retainer ring is snapped in a retaining groove 31 defined in the rotor shaft 3, so that the rotor shaft 3 is limited and cannot be detached. The outer peripheral of the rotor shaft 3 under the retainer 32 is fitted in an oil-impregnated bearing 2, and the oil-impregnated bearing 2 is placed in the inner hole of the axle tube 1 in a non-tight fit manner. The lower end of the axle tube 1 is then sealed by a lower cap 13, so that the oil-impregnated bearing 2 is retained between the upper cap 12 and the lower cap 13 for supporting the rotor shaft 3 to rotate.
However, the retainer 32 has a ring shape, and is snapped on the rotor shaft 3, therefore, the rotor shaft 3 needs to form a retaining groove 31 for positioning the retainer 32, thereby causing inconvenience in machining and assembling due to the ring-shaped retainer 32. In addition, the ring-shaped retainer 32 cannot efficiently prevent oil leakage.
The objective of the present invention is to provide a combination of an oil-impregnated bearing and a rotor, which can optimally prevent the lubricating oil from leaking, and the parts are easily assembled and machined.
The second objective of the present invention is to provide an oil-impregnated bearing combination, wherein the oil-impregnated bearing is placed in the axle tube in a non-tight fit manner, so that the inner peripheral of the central hole of the oil-impregnated bearing will not be deformed, therefore, the rotor shaft can be rotated smoothly, and thereby reducing noise of rotation.
The third objective of the present invention is to provide an oil-impregnated bearing combination which may prevent the lubricating oil from leaking, and prevent dust, impurities from entering the axle tube through the shaft seat, thereby prolonging the lifetime of the bearing.
According to the present invention, the axle tube whose upper end has an upper cap having an opening is secured in a tight fit manner inside the axle tube hole. After a rotor shaft extends through the opening of the upper cap, a retainer is snapped on the shaft. The retainer is provided with an annular wall protruding outward from the opening of the upper cap and rested on a shaft seat. The outer peripheral of the shaft under the retainer is sleeved with an oil-impregnated bearing, and the oil-impregnated bearing is placed in the inner hole of the axle tube in a non-tight fit manner. The lower end of the axle tube is sealed by a lower cap, so that the oil-impregnated bearing is retained between the upper cap and the lower cap, for supporting rotation of the rotor shaft.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.